Dose-dependent effects of in vivo antithymocyte globulin during conditioning for allogeneic bone marrow transplantation from unrelated donors in patients with chronic phase CML.

We conducted a dose-escalation study with antithymocyte globulin (ATG) in patients undergoing unrelated donor bone marrow transplantation (URD-BMT). This study analyzes the results for 97 patients with chronic myelogenous leukemia (CML) in first chronic phase. Median age was 36 years (16-51). In all, 40 patients were transplanted within 2 years after diagnosis and 57 later during disease. ATG-S (Fresenius) 20-120 mg/kg body weight (b.w.) was given prior to transplantation. A total of 31 patients received less than 60 mg/kg b.w. and 66 patients received 60 mg/kg b.w. or more. All patients except one were grafted with bone marrow, and graft-versus-host disease (GVHD) prophylaxis consisted of cyclosporin A and methotrexate. Graft failure did occur in one patient. Grade II-IV acute GVHD developed in 56.7% and extensive chronic GVHD in 11.3% of the patients. The relapse rate was 13.4%. With a median follow-up of 5.8 years (1.5-12.1), 5-year disease-free and overall survival for all patients were 56 and 66%, and for patients transplanted within 2 years of diagnosis it was 72 and 82%. A lower dose of ATG was a significant risk factor for poor outcome. In summary, URD-BMT remains an excellent treatment option for patients with early phase CML, if a sufficient amount of ATG is included in the preparative regimen.